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D. Dejour, P.G. Ntagiopoulos
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Trochlear dysplasia (roots from the Greek
words
“dys-”
: mal- and
“plasis”:
creation
[13]) is a developmental condition in which the
femoral trochlea lacks of its normal and
sophisticated concave anatomy, that is
absolutely necessary to engage the patella, and
instead, it becomes shallow, flat or even convex.
According to A. Amis [14], who published the
first biomechanical results on patellar instability
in trochlear dysplasia and the efficacy of
trochleoplasty procedures, it is recognized that
the mediolateral flattening of the anterior
surface of the trochlear facets results
predominantly from an
excess of bone centrally
in the groove
. In its major pattern it forms a
supratrochlear prominence or “bump” anterior
to the shaft of the femur, which the patella has
to override when the knee starts to flex in order
to engage in the groove for the remaining
degrees of flexion. Amis
et al.
showed that
simulated trochlear dysplasia led to significant
reduction in lateral stability and that by re-
creating a deep trochlear groove with a
deepening trochleoplasty procedure, lateral
stability increased significantly similarly to the
intact knee [14].
The genetic and primitive origin of trochlear
dysplasia and its familiar occurrence have
been shown by C. Tardieu and J.L. Jouve.
There is evidence that the asymmetrical
trochlear shape in adults exists in the foetus
since the third trimester of pregnancy,
something that could prove the genetic roots of
trochlear dysplasia [15, 16]. The shape of the
articular trochlea is variable in mammals
depending on their type of locomotion:
unguligrade, digitigrade or plantigrade [17].
The asymmetrical ingression of the patella into
the normal trochlea is a characteristic of the
modern man. Christine Tardieu’s extensive
anthropomorphometric studies on this field
have showed that the femoral valgus angle, the
femoral bicondylar angle and the morphology
of the normal trochlea and its articulation with
the patella are not present in prime mammals
or non-walking children and are the result of
human erect stance and bipedalism [17-19].
These anatomic characteristics of the trochlea
could have been integrated into the genome
during the course of evolution [17, 20].
According to Tardieu, the oblique angle of the
femur is the major feature, which initiated the
later modifications of the patellofemoral joint
that over 3 million years before, were never
inscribed in the human genome. The elevated
lateral femoral facet and the deep trochlear
groove are features that
“were first acquired,
then once selected, genetically assimilated,
and now appear on the foetal cartilaginous
epiphysis”
[17].
It is surprising that the origin of the study on
the abnormal trochlear shape in patellar
dislocation starts more than 200 years ago in
Europe. Although the term ‘dysplasia’ was not
originally used, the earliest reference on this
condition can be attributed to Richerand in
1802. According to Isermeyer [21], Richerand
made the very first description of the abnormal
morphology of the trochlear groove and the
lateral femoral facet in paediatric patients with
patellar dislocation. The interest on the
abnormal trochlear shape in (mainly)
congenital patellar dislocation is also
documented in the works of B. Pollard in 1891
[22] and D. Drew in 1908 [23], who focused
on the effects of a
“possibly congenital”
reduced lateral facet height on improper
patellar engagement and lateral patellar
dislocation, and even attempted to surgically
create a new groove for the patella. According
to S. Donell and C. Hing [24], in 1914, J.
Murphy also considered the shallow trochlear
groove as a cause for patellar dislocation, and
he performed a similar surgical correction by
burring the groove and adding fat tissue
between the patella and the femur to reduce
scarring and adhesions by the exposed
cancellous bone [25]. The next year, in 1915,
Fred H. Albee from the
“New York
Postgraduate Medical School Clinic”
, was the
first who tried to surgically correct trochlear
dysplasia properly with his pioneer procedure:
the lateral facet elevating trochleoplasty
(fig. 1) [26]. This was a completely opposite
concept and it included adding a bone graft
under the lateral facet in order to augment the
required mechanical block for a pathological
lateral patellar translation. This procedure
gained, for a period of time, overseas attraction
mostly in the U.K. and less in France.